1. Field of the Invention
The present invention relates to a picking device for a fluid jet loom and, more particularly, to a method of automatically controlling the respective jet patterns of subnozzle groups according to the actual running condition (that is, time of arrival) of a picked weft yarn.
2. Description of the Prior Art
U.S. Pat. No. 4,595,039 and EPO publication No. 0164773 (U.S. Pat. No. 4,673,004) disclose a method of automatically controlling the jetting period from the start to the end of a jetting operation of subnozzle groups on the basis of the result of an operation based on a measured weft yarn arrival time which is measured on the weft yarn arrival side of a loom. This prior art method regulates the jetting condition of the subnozzle groups according to the actual running state of a picked weft yarn, particularly, the running speed of a picked weft yarn, and hence stable picking operation is achieved constantly.
However, since this prior art method requires a complicated arithmetic operation by a microcomputer according to a complicated program for every controlling operation, the load on the microcomputer increases excessively when the microcomputer is used also for executing other control operations for controling the loom and restrictions are placed on programming realtime control processes.
It was found from experiments carried out by the applicant of the present application that the variations of the time of arrival of a picked weft yarn is not complicated and that the time of arrival can be classified into several typical running modes. This fact shows that no complicated arithmetic operation for every running mode of a picked weft yarn is necessary for every picking operation and suggests that practically optimum picking operations can be achieved by controlling the jetting operation of the subnozzle groups in several typical jetting patterns regardless of the variations of the physical properties of the weft yarn.
The picking device of an air jet loom picks a weft yarn into a shed by a main nozzle and assists the picked weft yarn in running across the shed by a pluarlity of subnozzles. Ordinarily, the subnozzles are divided into a plurality of subnozzle groups along the running path of the picked weft yarn and the subnozzle groups operate sequentially.
The jetting pattern of the subnozzle groups represented by jet starting time, jet ending time and jet period directly influences the running position of a picked weft yarn. Therefore, the running speed of the picked weft yarn must be taken into consideration in determining the jetting pattern. If the operation of the subnozzle groups is controlled in an inappropriate jetting pattern, the picked weft yarn is unable to run stably, the picked weft yarn will not be inserted satisfactorily, and compressed air is consumed excessively, thereby deteriorating the energy economy of the loom.